The use of mobile communications networks has increased over the last decade. Operators of the mobile communications networks have increased the number of base stations in order to meet an increased demand for service by users of the mobile communications networks. The operators of the mobile communications network wish to reduce the running costs of the base station. One option to do this is to implement a radio system as an antenna-embedded radio forming an active antenna array. Many of the components of the antenna-embedded radio may be implemented on one or more chips.
Nowadays active antenna arrays are used in the field of mobile communications systems in order to reduce power transmitted to a handset of a customer and thereby increase the efficiency of the base station, i.e. the radio station. The radio station typically comprises a plurality of antenna elements, i.e. an antenna array adapted for transceiving a payload signal. Typically the radio station comprises a plurality of transmit paths and receive paths. Each of the transmit paths and receive paths are terminated by one of the antenna elements. The plurality of the antenna elements used in the radio station typically allows steering of a beam transmitted by the antenna array. The steering of the beam includes but is not limited to at least one of: detection of direction of arrival (DOA), beam forming, down tilting and beam diversity. These techniques of beam steering are well-known in the art.
The antenna array or active antenna system is typically mounted on a mast or tower. The antenna is coupled to the base transceiver station (BTS) by means of a fibre optics cable and a power cable. The base transceiver station is coupled to a fixed line telecommunications network operated by one or more operators.
Equipment at the base of the mast as well as the active antenna system mounted on the mast is configured to transmit and receive within well defined limits set by communication standards.
The code sharing and time division strategies as well as the beam steering rely on the radio station and the antenna array to transmit and receive within well defined limits set by communication standards. The communications standards typically provide a plurality of channels or frequency bands useable for an uplink communication from the handset to the radio station as well as for a downlink communication from the radio station to the handset.
For example, the communication standard “Global System for Mobile Communications (GSM)” for mobile communications uses different frequencies in different regions. In North America, GSM operates on the primary mobile communication bands 850 MHz and 1900 MHz. In Europe, Middle East and Asia most of the providers use 900 MHz and 1800 MHz bands.
As technology evolves, the operators have expressed a desire for an active antenna product which is able to utilise the existing base-station investments, in addition to providing a new system/band. For example, in the roll-out of long term evolution (LTE) at 700 MHz (US) or 800 MHz (EU), the operators would like to deploy a single antenna at the masthead which could transmit the existing 900 MHz (EU) or 850 MHz (US) GSM signals, using equipment at the base of the mast, as well as providing active antenna functionality for the new LTE installation.
One solution could be to use a dual-band or broadband passive antenna, with two traditional base-stations at the foot of the tower. For example, the dual-band or broadband passive antenna would be mounted on a mast adjacent to a traditional base-station ‘hut’ or equipment cabin. This solution however would suffer various drawbacks. Having a dual band or broadband passive antenna would not allow the two bands to have independent downtilt angles. Both bands would need to share the same downtilt and this would be sub-optimal for either one or both systems, depending upon the tilt angle chosen.
It would be useful to combine existing RF signals, hereafter referred to as passive signal, emanating from (or travelling to) a base station or remote radio head at the bottom of a mast (for example) with signals from a different band, directly generated (or received) within the active electronics of an active antenna system.